Won't happen, and I don't believe it.  There is no possible way for anyone to keep their thumb straight and relaxed inside of a 15+ pound bowling ball.  There is no way that you can have your thumbhole tight enough that it will hold onto your thumb and still give you a clean release.  And there's certainly no way you can do this with a straight elbow and cupped wrist.  The textbooks can go to hell, it don't work.  Now if anybody can explain how I'm supposed to do this, I'll be forever indebted.  Forever.  I still haven't gotten around to ordering any Magic Carpet yet, but I'm hoping that I can fix the biggest problem first, which is me, most likely.  First of all, everyone has to bend their thumb a little, or else you'd just be holding on with the knuckle (front side of the hole, not the back).  Second, you can't relax your thumb in a 15 pound object, unless it's holding onto you.  And thirdly, like I've already said, there's no WAY you can get a clean release with a thumbhole being that tight to begin with.  Please help!!!
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Forget Kung Fu, I know Ron Bahr!!!

The only difference between youth and adult leagues are that the big boys are allowed to whine.  They're more entertaining anyway.

Boy did I get a lesson on the death grip. I though my arm was relaxed but it was not. I was squeezing way too much.

the guy did a few things. he told me to set up. them he checked if my fingers were tense or relaxed then he squeezed my biceps and then it it me on how tight I was holding on. even though it didn't feel like it.

next he had me take the ball with my hand in it and place it on top of a high surface(above waist) then told me don't hold on to the ball and walk backwards.

as soon as the ball fell off the countertop I stopped it. then he had me do this a few times until it fell by gravity and not me holding it back.

SO do you have to hold on to the ball with your thumb. yes. just way less than you think.

by the way the increase in speed was amazing compared to me doing nothing.
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"deserves got nothing to do with it."
-- William Munny

Yeah, that's kinda what I thought too!  I don't have a lot of speed at the release, but I think that my problem is my span is too long and I have too much reverse.  I'm at 1/4th reverse, which is pretty normal for my span length, but I'm thinking you're right.  Lol, I have a Hit that I haven't used much, and a plastic ball, so I might go to work on both of them.
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Forget Kung Fu, I know Ron Bahr!!!

The only difference between youth and adult leagues are that the big boys are allowed to whine.  They're more entertaining anyway.

Hamster, you work in a pro shop and you can't even get your own span right?  A quarter inch long, that's huge.

Well Hamster, for me, I bowl my best when the ball can hang freely by my side and my thumb relaxed and the only thing holding my thumb in there is the grip on the front of my thumb.  I think my hand being relaxed causes the muscles in my hand to try and contract more then they are when they are in my bowling ball.  My hand is just barely stretched when I'm holding my ball, and it causes the front of my thumb to just barely grip the thumb hole.  Rarely does this happen for me though, do to weather and thumb swelling and such.  I can usually get a clean release then because when the ball is moving at that speed at the bottom of my downswing, it comes off.  But yes, I think everyone has to squeeze a little.

As for people bending their thumb, it still doesn't seem natural for me.  If I need to grip the ball more, I tend to squeeze with the base of my thumb more then the tip, so I guess my thumb has always been kind of straight.  It's pretty rough though on the base of my thumb though, taking into account the number of times the skin just tears when my thumb swells too much.

And about shorter span, it does seem to help me from squeezing the ball.  I had a ball drilled about a year ago, and I think my span is about 1/16" shorter or so now and I tend to grip at that ball less.